CSERD


Example Verification Review


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The following is a verification review of the CSERD item GalaxSee located at

http://www.shodor.org/refdesk/Catalog/Item/44

"The model does not explicitly show the equations used in the model, and source code is not accessible. The model does, however, state the integration methods available in the solution, as well as the method of force calculation between gravitationally bound objects. The user has control over one approximation parameter, the shield radius, which is described in the documentation.

"Sample files were included with the program. Many of these were meant to be used with lesson plans packaged with the program that included expected solutions, so it was possible to compare a pre-created input file with expected results.

"Tests of the software's ability to run on the specified platforms were made on both Windows and Macintosh. For each integration method, the default time steps for default models resulted in little problems with conserving energy and momentum. Decreasing the time step did not result in substantial changes in the result, whereas an increased time step did cause error to occur. This is to be expected with models that use explicit integration methods.

"Exact comparisons of the Windows and Mac models were not possible, as the shield radius was handled in a slightly different way between the two versions. When the model for Mac was run against the model for Windows, the model results were practically identical, after the shield modification discrepancy was taken into account.

"In summary, this model did not include enough information about the base assumptions of the model or how they are implemented as code to directly apply verification tests, and one must rely on symptomatic tests. Examples are provided, the code runs on the stated platforms without obvious problems, and when the code is run with the default approximation parameters there are no obvious physical impossibilities.


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